Epithelial tissues have the critical responsibilities of defining a boundary between host and environment. This function includes the capacity of the tissue to protect against injury by acting as a barrier, to modulate the inflammatory response by regulating leukocyte influx, and to regulate molecular access by controlling salt and water movement. It is therefore pertinent that many of these same biologic functions have been ascribed to the metabolic products of fatty acid oxygenation pathways. Further support for autocrine and paracrine effects of fatty acid oxygenation products on epithelial tissues in general (and skin in particular) derives from the fact that epithelial cells on the surface of the skin contain active pathways for oxygenation of fatty acids, including arachidonic acid. In addition to cyclooxygenase and potential lipoxygenase activities, human epidermal cells express a novel regiospecific monooxygenase at a high level relative to other cell types. This proposal will examine the hypothesis that the activity of pathways controlling oxygenation of fatty acids, especially arachidonic acid, is critical for surface epithelial cell (i.e. keratinocyte) function in human epidermis. The proposed studies aim at determining the regulatory mechanisms of keratinocyte pathways for fatty acid oxygenation, and in particular, the recently discovered pathway for monooxygenation. The primary focus of the work is the human keratinocyte, but the studies will be supplemented when necessary by work on transformed human cells and epithelial cells from other mucosal surfaces (lung and gastrointestinal tract) that may express similar enzymatic activities and possess similar barrier functions. Definition of the critical biochemical determinants of epidermal oxygenase activity will lay the groundwork for regulating the function of the enzymes in intact tissue in health and disease. Specific aims are to: 1. Define the fatty acid oxygenation pathways expressed in human keratinocytes using analytical lipid chemistry, protein chemistry, immunochemistry, and molecular biology in freshly isolated and cultured epidermal cells and in epidermal tissue. 2. Determine mechanisms for the regulation of the proposed keratinocyte arachidonate 12-monooxygenase and cyclooxygenase (PGG/H synthase) using the same techniques in freshly isolated and cultured epidermal cells and in epidermal tissue.